The electrophotographic technique can instantaneously obtain a high quality image, and thus has been widely used as a copying machine, a printer, and a printing machine. As an electrophotographic photoreceptor (hereinafter, appropriately referred to as a “photoreceptor”) which is a core member of an electrophotographic process, a photoreceptor which uses an organic photoconductive material and has advantages of film formation without pollution and easy manufacture has been widely used.
On the other hand, in an electrophotographic system, image stability is inferior as compared with offset printing, particularly, in a case of printing a large number of images requiring delicate color reproducibility, many problems such as changes in color tone and image defects still remain to be solved.
Among them, the electrophotographic photoreceptor is repeatedly used in the electrophotographic process, that is, in a cycle of charging, exposing, developing, transferring, cleaning, erasing, and the like, and during the cycle, the electrophotographic photoreceptor is gradually deteriorated under various loads. Examples of such various loads include a high voltage load due to a corona charger which is commonly used as a charger and a chemical load due to strong oxidizing ozone or NOx which is generated at the time of discharge, an electrically conductive load due to a carrier generated by exposure, mechanical load due to a high voltage load, toner, a carrier, a paper component, or a cleaning member at the time of transfer, a photochemical load of a photosensitive layer composition due to erasing light or the light from the outside. For this reason, in order to suppress fluctuation in image properties in a case where the electrophotographic process is repeated many times, it is necessary to enhance resistance with respect to the aforementioned loads.
Since the printing is performed under various temperature and humidity conditions, it is required to have less influence on these temperature and humidity fluctuations. Among such requirements, a method for suppressing performance change with respect to humidity fluctuations by using hydroxygallium phthalocyanine as charge generation material of the photoreceptor has been widely used (refer to Patent Documents 1 to 3).
As means for improving the stability in use, Patent Document 4 discloses stabilization of surface lubricity, and Patent Document 5 discloses stabilization of light potential. Both of Patent Documents 4 and 5 disclose that the stabilization is achieved by using a high boiling point solvent for a charge transport layer.